A variety of D- and L-purine nucleoside analogs have been explored for use as immunomodulators. A class of nucleoside analogs that can have utility for such purpose are thiazolo[4,5-d]pyrimidine nucleosides, such as those compounds disclosed in United States Published Application No. 2005/0070556, assigned to Anadys Pharmaceuticals, Inc., the entire disclosure of which is incorporated herein by reference. These compounds include, for example, 5-Amino-3-β-D-ribofuranosyl-3H-thiazolo[4,5-d]pyrimidin-2-one of formula

A useful intermediate in the preparation of this and other thiazolo[4,5-d]pyrimidine nucleosides is the pyrimidine base, 5-amino-3H-thiazolo[4,5-d]pyrimidin-2-one of formula

It would be desirable to provide an efficient and cost-effective process for the preparation of this compound. The present invention provides such a process.